1. Field of the Invention
This invention relates to a safety system for limiting the speed of an engine, for example, when a fuel throttle is stuck open or the engine load is removed.
2. Prior Art
Engine driven machines, such as vehicles, and especially recreational vehicles, can create situations dangerous to the operator and others if an engine speed control or throttle is stuck in an open or high speed condition. For example, this is especially a problem with snowmobiles operated in a cold environment in which the throttle linkage or the carburetor for the engine can stick or freeze. Also, high engine speed can result from removal of the load on an engine; for example, when a drive belt breaks, or the vehicle overturns, or a gear shift is missed or if a drive propeller of a water vehicle is removed from the water. This can damage the engine or drive train and in some cases may cause the clutch to explode, endangering the operator.
Some vehicles have provided so-called "kill switches" for stopping the engine in a runaway situation, but this requires operator actuation and may not be satisfactory in a crisis situation. Also, when starting an engine, if the throttle is stuck in an open or high speed condition, engine speed reaches high rpm rapidly. In vehicles operated through a centrifugal clutch, the drive train is automatically engaged at a relatively low engine speed and the vehicle can move out of control, upon starting. While the throttle condition can be checked prior to startup, an operator often neglects to do so.
One approach to a solution of the above problem on snowmobiles is to provide two switches, one responsive to throttle actuation and one responsive to carburetor condition. If a carburetor element is stuck open after the throttle lever is released, the engine is killed by shorting the ignition coil. See U.S. Pat. No. 4,155,418. This approach requires carburetor modification. Also, the carburetor switch arrangement is insensitive to a no-load situation that does not involve an improper relationship between the carburetor condition and the throttle switch condition. Moreover, known limiting arrangements do not allow operation of the engine at a low or safe speed with a malfunction. As a result the operator cannot use the engine or drive the vehicle at all even in an intermittent manner. Once an engine is stopped, it may be difficult to restart and therefore killing the engine can result in an unsafe or hazardous situation in adverse environments, such as in a frigid environment where a snowmobile may be operated.
Other approaches to controlling engine operation have included cutting off engine ignition when the engine speed is greater than a throttle setting, but without more, these arrangements result in engine cutoff during normal deceleration. This causes accumulation of fuel in the exhaust system and subsequent backfire and can cause damage to the engine and exhaust system.